1. Field of the Invention
This invention relates to a technique of applying sugar coating on tablets etc., and particularly to a technique of sugar coating which contributes to uniform sugar coating and improvements in its finish.
2. Related Art Statement
It is conventional that, in order to apply sugar coating on tablets, pills and the like, materials to be coated such as the tablets, pills and the like are charged into an apparatus called a pan coating apparatus, and aqueous solution of sucrose is sprayed onto the material to be coated and dried while a pan, i.e., a rotatable vessel is rotated. The pan coating apparatuses used for that purpose include an open-type or semi-open type onion pan which has been used for a long time, and apparatuses which are provided with porous portions in the walls of the vessels for ventilating an accumulated layer of the material to be coated (for example, apparatuses put on the market by trade names of HI-COATER and AQUA COATER.
In these apparatuses, a member for agitating the materials to be coated, which is referred to as a "baffle" is mounted for the purpose of achieving uniform coating. Normally, such a type of construction is adopted that a plate-shaped protrusion is erected on an inner wall of the coating pan.
In contrast thereto, there is proposed an apparatus of a type having a fixed baffle (trade name: Static Baffle) which is inserted into the coating pan instead of being attached on the coating pan.
Namely, in Japanese Patent Publication No. 52-10665, there is shown a roof-shaped baffle consisting of two plate-shaped members, which have one side in common, is provided on an onion pan.
Furthermore, in U.S. Pat. No. 5,038,709 (EP Application Publication No. 355,771), there is disclosed an apparatus, in which a fixed baffle being displaceable in the vertical direction and variable in angle, is provided on a ventilating type coating pan.
Furthermore, in U.S. Pat. No. 5,033,405 (EP Application Publication No. 406904), there is described that a fixed baffle is provided on a polygonal coating pan.
Furthermore, in EP Application Publication No. 609,444, there is disclosed a device for rotating these baffle means.
In any one of the above-described known techniques, it is the premise that the baffle is fixed at a definite position while in one treatment stage.
Namely, in the above-described Japanese Patent Publication No. 52-10665, there is no suggestion that the position of the baffle is varied at all.
Furthermore, the apparatus of the above-described U.S. Pat. No. 5,038,709 is provided thereon with a baffle displacing means. In this U.S. Pat. No. 5,038,709, there is disclosed that displacement is made in accordance with the conditions of the process such as quantity of powdery/granular material and a stage of the process, and the baffle is displaced to a height above the layer of the treated material at the time of nonuse or its washing. However, this does not mean to displace the baffle during a stage of the process, but the baffle is held at a difinite position during a stage of the process. This is also true of the apparatus of the above-described U.S. Pat. No. 5,033,405. Further, also in EP Application Publication No. 609,444, no detailed disclosure about displacement of the baffle is given.
Thus, in the conventional technique, for the fixed baffle system, in which the independently movable baffle is provided separately from the coating pan, the mounted position of the baffle is changed for each batch stage of treating the material to be coated and, in the case of sugar coating, the volume of the material to be coated is increased gradually in accordance with the progress of process, whereby the baffle is displaced accordingly.
The fixed baffle system makes it easy to wash the coating pan, so that the working time can be shortened and the system is preferable also from the viewpoint of GMP (Good Manufacturing Practice) and the validation. However, in the case of the sugar coating, mixing effect is unsatisfactory as compared with the case of the baffle erected on the inner wall of the pan, whereby there are such disadvantages that there is large unevenness (deviation in weight) in coating quantity on the coated material and the finish is unsatisfactory. These disadvantages cannot be obviated even by displacing the baffle, for example, in accordance with the progress of process as described above.
When the present inventors studied the cause of the above-described disadvantages, such a fact was found that, in sugar coating, process of the gradual increase of the volume of the material to be coated does not smoothly proceed in accordance with the progress of the coating treatment, and, on the contrary, the increase of the volume follows serrated process in which the volume increases or decreases for each unit operation of one cycle in the coating processe, thus the volume in a same unit operation in a different cycle, i.e. stage increases little by little in accordance with the progress of the process.
The change in the volume during one cycle is very large, and, although it varies with conditions, it is usual that the volume change is as large as the volume change in a static state from the start to the end of the coating process. Accordingly, it is unsatisfactory to simply displace the position of the baffle in accordance with the treatment stage as in the conventional technique, and, the present inventors have found that, if there is no displacement of the baffle during the same treatment stage, then the baffle cannot be placed constantly at a proper position, so that the above-described disadvantages are presented.
In the ventilating type pan coating, the process of sugar coating consists of approximately 20 to 50 cycles (spray cycles) to repeat, each cycle consisting of three or four unit operations including spraying (or pouring) of syrup.fwdarw.Pause I (.fwdarw.Pause II).fwdarw.drying, to thereby gradually form sugar layers on the material to be coated.
In this process, during the time period from the halfway course of the spraying operation to the Pause I operation where the syrup is spreaded and coated uniformly on the surface of the material to be coated, the material to be coated is lumped together to be raised up due to the adhesion of the syrup, so that the volume of the material to be coated becomes very large. At that time, if the baffle is not displaced to the higher position, then the amount of the syrup adhering to the material to be coated becomes uneven, causing its surface to become rough.
In the Pause II, drying by cool air is performed and the adhesion is decreased, the volume of the material to be coated becoming gradually smaller. In the following drying operation, the volume returns to a state of being low and settled.
Even in the conventional coating pan such as the onion pan, substantially the same process is followed.